1. Field of the Invention
The present invention relates to a liquid crystal panel having a liquid crystal cell, a polarizer, and an optical element. Further, the present invention relates to a liquid crystal television and a liquid crystal display apparatus each using the liquid crystal panel.
2. Description of the Related Art
A liquid crystal display apparatus provided with a liquid crystal cell of in-plane switching (IPS) mode involves control of light transmittance (white display) and light shielding (black display) through application of an electric field in a horizontal direction on liquid crystal molecules aligned in a substantially horizontal direction without application of the electric field to rotate the liquid crystal molecules by about 45°. A conventional liquid crystal display apparatus provided with a liquid crystal cell of IPS mode has a problem in that a contrast ratio of a screen viewed from an oblique direction at an angle of 45° (azimuth angle of 45°, 135°, 225°, or 315°) with respect to an absorption axis of a polarizer degrades.
There is disclosed a technique for solving the problem involving use of a λ/2 plate exhibiting a refractive index profile of nx>nz>ny (wherein, nx, ny, and nz respectively represent refractive indices in a slow axis direction, fast axis direction, and thickness direction of a film) for improving display properties in an oblique direction (JP 11-305217 A, for example). However, the disclosed technique provides insufficient improvement in contrast ratio in an oblique direction and color shift in an oblique direction, and further improvement in display properties is desired.
An aromatic polymer film such as a polycarbonate-based resin, a polyarylate-based resin, or a polyester-based resin had been heretofore used as the λ/2 plate exhibiting a refractive index profile of nx>nz>ny (JP 04-305602 A or JP 05-157911 A, for example). However, the aromatic polymer film has a large photoelastic coefficient and its retardation values may vary easily by stress. Thus, the aromatic polymer film has a problem in that display evenness degrades as described below. In a case where the aromatic polymer film attached between a liquid crystal cell and a polarizer is exposed to high temperatures, retardation values may depart from designed values due to shrinkage stress of the polarizer. Further, uneven stress generated by heat of backlight may cause unevenness in retardation values.
Meanwhile, an aliphatic resin film such as a norbornene-based resin film has a small photoelastic coefficient. However, the aliphatic resin film hardly causes retardation, and desired retardation values cannot be obtained through stretching at a low stretch ratio as in the aromatic polymer film, or even at a high stretch ratio. The stretching at a high stretch ratio causes a problem of breaking of the film. Recently, further improvement in display evenness of a liquid crystal panel has been desired with increasing screen size and brighter backlight. However, the conventional technique as described above cannot provide a liquid crystal panel sufficiently satisfying the requirements.